The present invention relates to centrifugal clutch assemblies for use in recreational vehicles, and particularly to a roller for engaging a pivotable drive arm in a centrifugal clutch assembly. More particularly, the present invention relates to rollers appended to a fixed base of a centrifugal clutch assembly having drive arms that pivot under the influence of centrifugal force to act against the rollers to actuate a variable-speed pulley included in the centrifugal clutch assembly.
Recreational vehicles such as golf carts, snowmobiles, and go-karts are typically provided with a centrifugal clutch assembly that includes a variable-speed pulley. The variable-speed pulley is connected to an engine shaft and typically includes a fixed pulley flange mounted on the engine shaft and a movable pulley flange that is able to slide back and forth along the longitudinal axis of the engine shaft. Typically, a drive belt lies in a V-shaped groove defined between the fixed and movable pulley flanges. When the pulley flanges are closer together, the drive belt is turned at a higher speed. When the flanges are further apart, the drive belt is turned at a lower speed. See, for example, U.S. Pat. No. 3,759,111 to Hoff for a description of a centrifugal clutch with such a variable-speed pulley.
A variable-speed pulley of the type disclosed in the Hoff '111 patent typically is actuated to increase the speed of a drive belt coupled to the variable-speed pulley by a plurality of centrifugal drive arms mounted for pivotable movement on a circular movable pulley flange of the variable-speed pulley and arranged to lie in spaced-apart relation around the circumference of the circular movable pulley flange. Typically, such pivotable centrifugal drive arms swing outwardly away from the longitudinal axis of an engine drive shaft during rotation of the variable-speed pulley about the longitudinal axis of the engine shaft on which the variable-speed pulley is mounted. The drive arms act against rollers mounted for rotation on a base that is fixed to the engine shaft. The action of the drive arms against the rollers causes the movable pulley flange to move axially along the longitudinal axis of the engine shaft toward the fixed pulley flange.
A tip end of each centrifugal drive arm is configured to engage and "push off" against one of the rollers mounted on the fixed base during operation of the centrifugal clutch. This push-off action is sufficient to urge the movable pulley flange in a direction toward the fixed pulley flange while the drive belt lies in the V-shaped groove defined between the movable and fixed pulley flanges so as to narrow the width of the V-shaped groove and increase the speed of the drive belt. Thus, pivoting movement of the centrifugal drive arm against the rollers functions to "actuate" the centrifugal clutch so as to change the speed of a drive belt engaging the variable-speed pulley in the centrifugal clutch.
Typically, roller assemblies are mounted to a fixed base in spaced-apart relation and are arranged to oppose the pivotable drive arms. For example, U.S. Pat. Nos. 5,326,330 to Bostelmann; 4,483,686 to Kobayashi et al.; 3,961,539 to Tremblay et al.; 3,861,229 and U.S. Pat. No. 3,777,584 to Domaas; U.S. Pat. No. 27,858 to Laughlin; as well as Canadian Patent 985,931 and Japanese Patent No. 58-102,852 to Kobayashi all disclose clutches including rollers for use with pivotable drive arms. Rollers of this kind are well-known. For example, U.S. Pat. Nos. 5,154,673 to Fukunaga et al.; 4,938,610 and 4,881,828 to Kato; as well as Japanese Patent No. 60-201,162 to Shimizu, French Patent No. 614,387 to Ballot, and a journal article in S. A. E. Journal (Transactions), vol. 41, no. 4, pp 480-81 all disclose rollers, some of which are for use in centrifugal clutches.
One type of design for a roller assembly is disclosed by Japanese Patent No. 60-201,162 to Shimizu. This type of roller assembly includes a ring-shaped member connected to the outer periphery of a bearing by press fitting two steel bearings to the inner peripheral side of the ring-shaped member. The bearings include an interior surface that is arranged to engage a pin extending along the longitudinal axis of the roller assembly.
There is inherent variability associated with the magnitude of the inner diameters of any group of ring-shaped members as the result of factors related to the production of ring-shaped members, and there is inherent variability associated with the magnitude of the outer diameters of any group of bearings as the result of factors related to the production of bearings. The variability of the inner diameters of the ring-shaped members and the variability of the outer diameters of the bearings can cause the fit of some bearings in some ring-shaped members to be too tight and other bearings in other ring-shaped members to be too loose. Both of these unfavorable tolerance combinations, typically referred to as "unfavorable tolerance stack-ups", can result in scrap or premature failure of the roller during use.
What is needed is a roller assembly for use in opposing a pivotable drive arm in a variable-speed centrifugal clutch, the roller assembly being easy to assemble, inexpensive to produce, and including a minimum number of parts. Vehicle manufacturers would appreciate a roller that is configured to minimize unfavorable tolerance stack-up problems of the type that can affect roller sleeves and bearings in conventional rollers, thereby minimizing scrap and wear of the roller and its companion centrifugal drive arm.
According to the present invention, a centrifugal actuator is provided for a centrifugal clutch having an axially fixed base and an axially movable pulley flange. The actuator acts between the fixed base and the movable pulley flange. The actuator includes a drive arm having a camming surface and a bottom that is pivotably attached to the movable pulley flange, a mounting pin coupled to the fixed base, and an improved roller that rotates about the mounting pin and that has an outer surface that engages the drive arm.
The roller includes a cylindrical outer sleeve having a side wall formed to include an outer drive arm-engaging surface engaging the camming surface of the drive arm. The side wall of the outer sleeve defines an interior region. A cylindrical inner sleeve is received by the interior region. The cylindrical inner sleeve includes a side wall having an outer surface coupled to the cylindrical outer sleeve and an inner load-bearing surface engaging the mounting pin.
In preferred embodiments, the roller in accordance with the present invention is mounted to a base that is fixed to an engine drive shaft. The centrifugal clutch includes three circumferentially spaced-apart actuators and each actuator includes a pivotable drive arm having a camming surface. The camming surface of each drive arm engages one of the rollers.
The drive arms are mounted on a movable pulley flange that can slide axially along the engine drive shaft relative to a fixed pulley flange and that can rotate about the engine drive shaft. Centrifugal force created by rotation of the movable pulley flange at a speed in excess of a certain speed causes each drive arm to swing radially outwardly from a static inward position to an outward position. As the rotational speed of the movable pulley flange increases, the drive arms push off against the rollers and swing outwardly causing the movable pulley flange to slide along the engine drive shaft from a lowest-speed position far from fixed pulley flange to a highest-speed position near the fixed pulley flange.
Each roller in accordance with the present invention includes an outer sleeve and an inner sleeve coupled to the outer sleeve. The inner sleeve of the roller includes an interior load-bearing surface defining a cylindrical interior region of the roller. Each outer sleeve includes a drive-arm engaging surface that frictionally engages the camming surface of the drive arm so that the roller rotates as the drive arm swings outwardly and inwardly. The load-bearing surface of each roller engages a mounting pin connected to the base fixed to the engine drive shaft and slides around the mounting pin as the roller rotates relative to the mounting pin.
Also in preferred embodiments, the outer sleeve is a cylindrical steel sleeve and the inner sleeve is made from a plastics material. The steel sleeve provides a wear-resistant drive arm-engaging surface that also distributes the load resulting from engagement between the drive arm-engaging surface and the drive arm across the length of the roller. The drive arm-engaging surface of the outer steel sleeve cooperates with the tip of the drive arm to provide enough friction therebetween to ensure that the roller rotates in response to pivoting movement of the drive arm.
The inner sleeve of each roller is preferably injection molded directly onto its companion outer sleeve. Injection molding the inner sleeve onto the outer sleeve involves fewer manufacturing steps than producing a separate inner sleeve and subsequently inserting the separate inner sleeve into the interior region of the outer sleeve.
In addition, a member in the injection mold establishes the size and shape of the interior bearing surface of the inner sleeve that engages the pin, so that the bearing surface in each roller is of a consistent size and shape regardless of the size or shape of the interior surface of the cylindrical outer sleeve. As a result, the variability of the inner diameters of the inner sleeves among a group of rollers is minimized when the inner sleeves are formed from an injection molded plastics material.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.